1. Field of the Invention
The present invention relates to an actuator, an optical device with the actuator, and an optical recording/reproducing apparatus with the optical device.
2. Description of the Related Art
The recording density and reproducing speed of optical recording/reproducing devices are steadily increased. Particularly, with the increasing demand for high-resolution moving pictures, optical disks with great storage capacity are required.
Recently, optical systems with blue laser diodes (BD) are introduced. Such a blue-laser optical system has a high numerical aperture (NA=0.85) and a shot wavelength (405 nm).
FIG. 1 is a schematic view of an optical pick-up system employing a blueray disk.
Referring to FIG. 1, the optical pick-up system includes a blue laser diode 101 emitting a blue laser beam, a beam splitter 102 reflecting or transmitting the laser beam incident from the blue laser diode 101 according to the polarization of the laser beam, a collimator lens 103 converting the laser beam coming from the beam splitter 102 into a parallel beam, an object lens 104 condensing the parallel beam onto an optical recording medium 105 and transmitting the beam reflected from the optical recording medium 105 to the collimator lens 103, and an optical detector 106 generating an electrical signal in response to the beam reflected from the beam splitter 102.
As shown in FIG. 1, the laser beam emitted from the blue laser diode 101 is transmitted through the beam splitter 102 and converted into a parallel beam by the collimator lens 103 for projecting the parallel beam onto the object lens 104. The object lens focuses the incident parallel beam to a single point on the optical recording medium 105 for recording and reproducing data.
The beam focused onto the optical recording medium 105 is reflected to the optical detector 106 through the object lens 104, the collimator lens 103, and the beam splitter 102. The optical detector 106 converts the reflected beam into an electrical signal.
Here, the optical recording medium 105 includes two layers on its disk for a high data density and capacity.
That is, since the blue lay disk uses a light source having a short wavelength, spherical aberration arises due to the deviation of a disk cover layer or the respective layers. Sometimes, the spherical aberration exceeds an allowable limit.
Particularly, to compensate for the spherical aberration due to the deviation of the respective layers, an optical unit is provided in an optical path for offsetting.
Therefore, a beam expander is provided in an optical path, and an optical unit is provided on an optical axis for compensating the spherical aberration. That is, a uniaxial servo system is required to move a lens of the beam expander.
FIG. 2 is a view of a uniaxial actuator for compensating for a spherical aberration according to the related art.
Referring to FIG. 2, a uniaxial actuator 110 for compensating for spherical aberration includes a movable unit 111 formed with a lens 113 of a beam expander at a center portion, a motor 113, a lead screw 114 rotating by the motor 113, and a shaft 115 guiding the movement of the movable unit 111 according to the rotation of the lead screw 114.
Here, the beam expander includes a combination of a first lens and a second lens. The first lens is a concave lens, and the second lens is a convex lens. In FIG. 2, the lens 112 is a convex lens or a concave lens. By moving the lens 112, a beam diverging angle or a beam converging angle can be adjusted according to the distance between the two lenses.
The movable unit 111 has to be moved along an optical axis to compensate for the spherical aberration using the lens 112. When the motor 113 operates, the lead screw 114 connected to a motor shaft is rotated to move the movable unit 111 back and forth. Further, the shaft 115, which is disposed in the movable unit 111 at an opposite side to the lead screw 114, guides the movement of the movable unit 111, such that the spherical aberration can be compensated for according to the variation of the distance between the two lenses.
However, since the lead screw 114 connected to the motor shaft is located in one side of the movable unit 111, a driving force may be concentrated on the one side of the movable unit 111.
Further, the lead screw driving method requires the motor-screw system additionally, thereby increasing cost and complicating the assembly process.
Furthermore, the uniaxial actuator characteristically requires a highly precise driving to operate for the compensation for the spherical aberration. Therefore, angular distortion must be minimized during operation of the uniaxial actuator to keep the operating precision blew tens of micrometers and secure the tilt margin of the optical unit.
If an additional servo system is used for improve the operation precision, an additional circuit system is also required for a real-time feedback of position information.